If it is placed on the hour hand, you can easily get by with winding once a day. The farther down on the gear train, the slower it will unwind. You want it farther down the gear train so you aren't winding the clock every 4 hours. Placement of the weight and cord is a little critical. This isn't very practical unless you want to pretend you are in a time machine. If this was just the weight and gears, when the weight was released, the gears would spin for a few seconds and the weight would hit the floor. As it pulls down, it rotates the gears causing the minute and hour hands to rotate. The weight is wound around one of the axles. It uses a weight as the energy source, and a pendulum to regulate how fast this energy escapes. These have been in existance since the mid 1600's. This type of monitoring using the CDT is best done by a health care professional.įinally, the often asked question: “What will happen to the generation of kids who have grown up with digital clocks?” Well, for them, this test may indeed become obsolete. However, we still have many more years of the current cohort of middle-aged and elderly people for whom this test will still be useful.The clock I have designed is a basic pendulum clock. Importantly, it also establishes a baseline for future monitoring to determine if cognitive impairment is worsening and thus increasing the likelihood of an underlying dementia. The clock test is frequently used in combination with the MMSE as a screening battery.Ĭlock-drawing is, of course, subject to the same limitations as all screening tests, including the MMSE. It is affected by level of education and should not be used alone for diagnostic purposes or for assessing the severity of cognitive impairment. However, like all good screening tests, it does tap into multiple cognitive functions and can provide a ‘signal’ that calls for further inquiry or more investigations. Also, the visual impact of abnormal clocks is often an eye opener for families who may not have been aware of the full extent of cognitive dysfunction. It is as sensitive to cognitive impairment as the MMSE and picks up changes in cognition over time. Moreover, it tests frontal-executive, higher-level brain functioning (planning and abstract ability) in a way that the MMSE does not. It takes less time to administer and is generally very well accepted. It turns out that clock-drawing correlates very well with the MMSE. Drawing a clock requires multiple cognitive functions (not just visuospatial ability). It requires: visual memory of a clock, planning ability and concentration in order to place the numbers evenly around the clock circle, abstract ability to set the time using the symbol of hands which point to the number ‘2’ to represent 10 minutes past the hour. The latter task is very sensitive to cognitive impairment as affected individuals often ‘pull’ the minute hand to point to the number ‘10’ rather than ‘2’. The CDT’s acceptability, shorter time (2 minutes), and ease of administration have made it very popular. Originally, the clock-drawing test was cited in a leading neurology textbook as a means of specifically assessing parietal lobe function in the brain, because that is the location of visuospatial ability. However, in the 1980s, our group at Sunnybrook (among others) began using the clock-drawing test and assessing its value as a broader cognitive screening tool comparable to the widely used Mini Mental State Examination (MMSE). The MMSE is a 30-item test that assesses orientation to time and place, attention, short term memory, verbal skills, and visuospatial ability. How did this particular test achieve such popularity among clinicians and why is it so useful? The test uses a pre-drawn circle and consists of asking the patient to put in the numbers of the clock and then to set the time to ‘10 past 11’. The clock-drawing test (CDT) has become one of the standard cognitive screening tools used around the world. Like all cognitive screening tests, it is designed to detect early brain changes to determine if an individual may be suffering from a form of dementia.
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